1. Field of the Invention
The present invention relates to a process for increasing the water solubility of gypsum by treating the gypsum with concentrated sulfuric acid. The reaction product is useful for treating soils.
2. Description of the Related Art
Anhydrous calcium sulfate occurs in nature as the mineral anhydrite. The dihydrate, or gypsum (CaSO.sub.4.2H.sub.2 O) is, however, more common. The groups of gypsum products include calcined building materials. Calcined gypsum is employed in making wallboard and various other products.
Calcium sulfate is soluble in 375 parts cold water or 485 parts boiling water. Its solubility in water is increased by acids, ammonium chloride, or nitrate; it is diminished by magnesium sulfate. The Merck Index, p. 198 (7th Edition 1960). The U.S. Department of Agriculture 1957 Yearbook entitled "Soil" also refers to the solubility of gypsum at page 286, paragraph 2. In particular, the rate of reaction of gypsum is limited only by its solubility which is about 0.25%. Under field conditions, the application of three- to four-acre feet of irrigation water is required to dissolve four or five tons of high grade agricultural gypsum. In this regard, there are 2,715,400 pounds of water, or 325,978 gallons of water, to one-acre foot of water.
As a result of these properties, gypsum has a very limited degree of water solubility. Gypsum also has a very restricted reactivity especially with respect to its agricultural application to soils.